1. Field of the Invention
The present invention relates to a conveying apparatus in which an unit for supporting a conveyed object is suspended by a belt so as to be lifted and lowered by winding and unwinding the belt extending from a traveling unit for transportation.
Priority is claimed on Japanese Patent Application No. 2005-206975 filed Jul. 15, 2005, the content of which is incorporated herein by reference.
2. Description of Related Art
In a configuration of a conveying apparatus (conveyer) wherein an unit for supporting a conveyed object (load) is suspended by windable belts so as to be lifted and lowered by winding and unwinding the belts fed from a traveling unit for transportation provided with winding rollers for winding and unwinding the belts. A belt fed from the winding roller is guided by a guiding pulley at a fixed position and is suspended to a downward direction. At that state, the support unit is suspended at the end of the belts. Conventionally, in conveying apparatus of this type, for example, as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-11299, a flanged pulley that have flanges holding the belt from both width directional sides of the belt has been utilized as the guiding pulley for downwardly suspending the belt. In this case, in order to reduce size and weight of the conveying apparatus, and reduce costs, it is usual for the flanged pulley to be configured to have smaller diameter than the winding roller
In a conventional configuration of the conveying apparatus that utilizes a flanged pulley as a guiding pulley for downwardly suspending the belt, dust is generated by wear of the belt at the position of the flanged pulley. Therefore, the conventional type conveying apparatus cannot be used in working environments requiring dust-free clean atmosphere, for example, in a clean room for semiconductor production.
In conveying apparatuses of this type, a flanged pulley having flanges that hold the belt from both width directional sides of the belt is also utilized as a winding roller for winding and unwinding the suspending belt. This winding roller has a large diameter because of requirement for winding a long length of a belt. On the other hand, in order to satisfy a demand for reducing cost, and for downsizing and weight saving the conveying apparatus, a flanged pulley as a guiding pulley for downwardly suspending the belt is usually configured to have as small a diameter provided that an overstress is not caused in the belt to be guided. In such a configuration, the circumferential speed of the guiding pulley is remarkably faster than the circumferential speed of the winding roller. Therefore, regarding a relative sliding rate between the flange and the side edge of the belt departing from the rotating body in the tangential direction, the relative sliding rate at a position of the guiding pulley is extremely higher than that at a position of the winding roller. Therefore, regarding a sliding friction causing generation of wear dust originated from side edges of the belt, sliding friction between the belt and the flanges of the winding roller scarcely or do not cause a wear dust, whereas a sliding friction between the belt and the flanges of the guiding pulley remarkably cause a generation of wear dust. As described-above, dust generation is considered to be an obstruction to the use of conveying apparatus in clean rooms. The present invention has an object of providing a conveying apparatus by which the above-described conventional problems can be solved.